Due to the detrimental effects refrigerant has on the environment, it is illegal to handle it without the necessary certification. You also risk serious injury if you come into contact with the escaping gas. You should leave anything to do with the refrigerant to a qualified professional, who will be able to evacuate the system and dispose of the gas in an environmentally-safe manner.
If your aircon is not working, because the condenser or pipework, has been punctured and all gas has escaped, you may consider changing these components yourself, prior to visiting a specialist for regassing. As it is illegal for an airconditioning engineer to recharge a system that is known to be leaking, it will be vacuum- or pressure-tested first using inert nitrogen gas. Only if the system does not lose pressure will it be recharged with the correct type and quantity of gas and oil. However, small leaks in an air-conditioning system can be tricky to locate and a low-pressure switch will deactivate the compressor clutch, or internal solenoid, even though the system contains residual pressure.
Aside from the safety, environmental and legal implications, opening-up the air-conditioning system, or allowing it to depressurise completely, is not advisable, because external contaminations can enter the system, resulting in reliability issues. Furthermore, the receiver/dryer could become oversaturated with moisture from the air, rendering it useless.
While replacing pipes and condensers at home is possible, provided you have the system evacuated of any residual gas by a professional first, a novice DIYER is restricted to periodic maintenance duties, most of which are on the ‘dry’ side of the system. More experienced home mechanics will need slightly more advanced diagnostic equipment to obtain live data readings that can pinpoint specific problems – this is useful on cars with complex climate control systems.
While many of the aircon components are accessible, you need to remove the heater box to reach the evaporator, which could mean extensive dismantling of the interior – it is not as difficult as it looks.